Focus Traversal in forms seems to be vertical only

Focus Traversal in forms seems to be vertical only

I've created a simple two column form like this:





But I find that when I use / preview the form, the "focus traversal" is not horizontal but vertical.
When using the form, after I fill the value for the left field of the first row, and I hit the tab key, the focus goes to the left field on the second row, instead of the right field of the first row.

I think this is not intuitive, and I can't seem to find a way to make focus traversal be horizontal rather than vertica.

¿What can I do about this?